Means for detecting the defective element in a series connection



G- S. OVREVIK Jan 20, 1959 MEANS FOR DETECTING THE DEFECTIVE ELEMENT IN A SERIES CONNECTION Filed May 18. 1954 VOLTAGE SOURCE R mm, mm v WE 1R v o N N% E L G United States Patent MEANS non DETECTING THE DEFECTIVE ELEMENT IN A-sniuns CONNECTION Glenn 5. Ovrevik, Washington, D. (3. Application May 18,1954, Serial No'. 430,537

3 Claims. (Cl. 1315-92 This invention relates in general to low" impedance filamentary elements in aserial electrical connection and in particular-to a means for the detection'of defective elements.

Serially connected lighting systems are well known in the decorative display art. They have found, due'to their simplicity and economy, their most popular application in Christmas tree-lighting systems. Such systems generally employ low wattage lamps which permit, in addition to economical operation, the more decorative design of the bulb structure. Unfortunately, series systems possess an inherent disadvantage in that when one lamp burns out not only the defective lamp, but all others in the string are also extinguished. Heretofore, a tedious substitution of lamps has been the only practical means to locate the'defective lamp. It has been well recognized that the servicing of series connected systems on the tree requires aconsiderable amount of dexterity and patience.

-It is an' object of this invention to provide a quick, simple and effective means for the detection of defective low impedance filamentary elements in a serially connected system.

It is another object of this invention to provide a means for the detection of defective lamps in a serially connected Christmas tree lighting system which will not substantially increase the wattage of such a system.

It is a further object of the invention to provide a means for the detection of defective lamps in a serially connected system which may be simply and cheaply manufactured.

It is still another object of this invention to provide a safe means for the detection of defective lamps in a serially connected Christmas tree lighting system.

It is' an additional object of this invention to provide a means for the detection of defective lamps in a serially.

connected Christmas tree display which is inexpensive to operate in conjunction with said display system.

Other objects of this invention Will become apparent from a complete understanding of the invention for which reference is had to the accompanying drawings and description.

Figure l is'a schematic diagram of a plurality of lamp assemblies embodying the detecting means of this invention.

' Figure '2 is a cross sectional View of one embodiment of the invention in which the detecting means is incor porated in a lamp socket.

Figure 3 is a cross sectional view of a further embodiment of the invention in which the detecting means is incorporated in a lamp socket.

Figure 4 is a cross sectional view of another embodiment .of the: invention in. which the detecting means is incorporated-in a lamp base.

' Briefly, this'invention provides a simple means for the detection-of a defective element in an electrical circuit comprising a plurality of series connected low impedance filamentary elements. In this invention'aheating element of relatively high impedance is shunted across each 2,870,377 Patented Jan; 20, 1959 "ice low impedance element and is substantiallyiout'ofithe circuit when the low impedance element is operative. When the filament burnsout in any. of the serially con nected filamentary elements its respective heating element becomes an active part of the serial connection to dras tically' change the voltage distribution in the circuit and reduce the current in the circuit.

appears across the heating element associated with the perception of the increase in temperature;

ment. By'simply checking the circuit for an'observable' heating. by touchingv the" various elements, the'bnrnt out element may be readilyzlocated.

Referring now to the drawings; Figure 1 shows. aplu rality of lamp filaments, 10, connected'in series across a voltage source'lfi'. Lamp filamentslli are characterized bya low impedance and may be of the typefound in standard Christmas tree lamps for 8 in a st-ringseries connection. Such lamps generally have a cold resistance of approximately 70 ohms. The voltage source may be a standard 115 v. household outlet of the type found in modern American homes. A- separateheatingelement;

12,15 shown electrically connected in parallel with each.

filament 10 as'a part ofthe lamp assembly. This heat ingelei'n'ent has a relatively high impedance 'which, for

purposes-of illustration, may be 15,000 ohms: Inthis type of'circuit, when all filaments are lit a maximum current flows in the circuit and an equal voltage distribu tion exists amongthe lamp assemblies. In the typical 8- in a string arrangement illustrated, the maximum circuit current would be about .25 amps and each lamp would drop about 14 volts; With 14 volts acrossthe 70 ohm" filament, 10, and 15,000 ohm heating element in parallel, only a negligible amount ofcu'rrent, in theneighborhood of .0009 amps, will flow in the heating element to dissipate approximately 4 of a Watt. When one filament in the string burns out, its associated heating elementTZ becomes an important factor in the series circuit and the" resistance of the circuit is increased to 15,490 ohms, in this particular illustration, to reduce circuit current to a minimum. Thus, approximately of the source voltage 11 is suddenly dropped across the heating element associated with the burnt out lamp and the remaining lamps, dropping less than 1 volt apiece, are extinguished andcool down.

of a watt. This dissipation, in the form of heat produces an observable temperature rise, which differentiates thiselem'ent from the now cooled remaining elements, to disclose the location of th'edefective lamp. By disposing the heating element 12 in close heat conductive relation to each filament, the defective lamp maybe easily detected by simply touching the lamp assembly containing the defective lamp.

in the 8 in a string Christmas tree lighting systems illustrated, each-lamp dissipates approximately 3.5 wattswhen the circuit is in operation and, as mentioned pre viously, each heating element in shunt dissipates a mere It is & of a watt for a total dissipation of 28 watts. obvious, therefore, that the cost of operating a series Christmas tree lighting system, which is considerably less than the cost of any other lighting system, remains substantially the same with the incorporation of the defee rive lamp'dete'ction' convenience'of the invention.

In Figure 2 a lamp receptacle, embodying the inven- In the new voltage distribution, substantially the entire voltage of the circuit The new minimum current in the cir-' cuit, in the neighborhood of .0075 amps, increases the energy dissipation of the heating element from 4 to tion, is shown in cross sectional view. For purposes of illustration only, the lamp receptacle comprises an insulating shell 14, which may be made of plastic, surrounding a cylindrical lamp socket having an isolated center terminal and a metallic wall 16 which forms a second terminal. Each of said terminals are provided with fiexible conductive leads 17 and 18, respectively, for connection to similar lamp assemblies in the manner shown in Figure l. The center terminal 15 is separated from the outer terminal 16 by a supporting member 19 which in this embodiment constitutes the heating element of the invention. The supporting member 19 has a disc configuration and a determined impedance measurable between the center and the periphery of the disc. It is not essential, however, that the heating element have a disc configuration. For example, the shell 14 may be enlarged to enclose a rectangular heating element 19 which supports and separates the terminals. It is essential that the heating element be electrically connected across the two terminals to permit it to be energized. A carbon composition or any other rigid resistive material may be used for the supporting member 19. It is understood the lamp socket of this embodiment may be adapted to retain the screw base shown, a bayonet or any other type lamp base retaining means.

Figure 3 shows another lamp receptacle embodying the invention in cross sectional view. For purposes of illustration only, the lamp receptacle in this embodiment comprises a shell 2!) surrounding a cylindrical lamp socket having a center terminal 21 and a non-metallic wall 22 adaptable to retain a screw or bayonet type lamp base. A metallic ring 23, substantially the diameter of said wall 22, is contiguously disposed above said wall and within the shell to form a second terminal of the lamp receptacle. Each of said terminals are provided with flexible conductive leads 24 and 25, respectively, for connection to similar lamp assemblies in the manner shown in Figure 1. The center terminal 21 is electrically connected to the shell 20 at the diametric center of its base. The ring terminal 23 is electrically connected to the shell 20 along the periphery of the shells upper edge. The shell 20 in this embodiment constitutes the heating element of the invention and has a determined impedance measurable between termnials 21 and 23. The shell 20 may comprise a carbon composition or any other rigid resistive material as in the case of element 19 in the embodiment of Figure 2. In this case, however, a heating may more readily be detected in the outer shell and less heat dissipation is necessary, thus the shell may have a higher impedance, for example 20,000 ohms. it is not essential to this embodiment that the entire shell 29 be utilized as the resistive element, provided the portion of the shell utilized electrically shunts the lamp filament. In this embodiment it is desirable as a safety measure to coat the exterior of the shell 20 with the thin layer of electrical insulating material indicated by 26 in the drawmg.

In Figure 4, a lamp base, which embodies the invention, is shown in cross sectional view. For purposes of illustration only, the lamp base has a typical bayonet type construction which comprises a cylindrical metallic wall 27, having 2 diametically opposite protrusions for the retention of the base in the bayonet type receptacle shown, and an isolated center terminal 23. The wall 27 is provided with a cementitious inner shoulder 29 which supports and retains the neck of the evacuated bulb which in turn supports the filament 31 by means of conductive leads 32 and 33. Said bulb and filament may be a typical Christmas tree lamp, of the type described in connection with Figure 2. The filament is electrically connected through the glass envelope of bulb 30 to the two terminal structure, metallic wall 27 and the center terminal 28, by means of said leads 32 and 33, respectively. Center terminal 28 is separated from the wall .27 by a rigid resistive material 34 which in this embodiment 4 constitutes the heating element of the invention. This material 34 may be a carbon composition having a determined impedance measurable between its center and its periphery.

While only screw type and bayonet type lamp assemblies have been shown in the various embodiments this invention is not restricted, of course, to these two types of assemblies. In general most Christmas tree lighting systems use screw base bulbs and, as is well known, these bulbs frequently become loose in the socket to extinguish the string. This annoyance may be avoided by the use of the more secure bayonet type lamp base shown in Figure 4. This type lamp assembly is particularly desirable and may be readily adapted to incorporate the detection means of this invention in the lamp base embodiment of Figure 4. The socket embodiments of this invention may also be adapted to retain a bayonet type base but the spring mechanism in the socket may make it more expensive to produce on a mass production basis.

In each of the embodiments of this invention the impedance of the heating element must be determined by the peculiar heat energy dissipation and the heat conduction characteristics of the particular low impedance element assembly, in other words by the heat necessary to produce a sensuously observable temperature, for example, 55 C. Such a temperature may be readily detected by touch. Obviously the heat conductive characteristics will vary for different material used both in the heating element and in the assembly and for the location of the heating element in the assembly. Therefore it is under stood that it is within the purview of this invention to employ any high shunting impedance necessary to produce an observable heating effect.

As pointed out in the discussion of each of the various embodiments, a composition resistance may be used as the heating element of this invention. Moreover, in view of the fact that they may be mass produced and are therefore relatively inexpensive, their use is highly desirable in the present invention. The selection of the proper type of composition resistance involves several considerations. Such resistances generally constitute a conducting material, such as carbon, mixed with a filler, which serves as a diluent, and combined with some type of binder. As is well known, their exact resistance is relatively unstable and particularly subject to humidity conditions unless they are suitably protected. This is primarily due to the use of an organic binder and, although the exact resistance is not particularly important in the present invention, it is advisable to employ a composition resistance having a non-organic binder to insure a reasonably stable resistance over a period of several years. Composition resistances are also known to decrease in value with increasing voltages but this ettect is generally not objectionable within the normal voltage rating of the resistance. In this invention the voltage across the heating element should never exceed the rated voltage. It should be pointed out that in the illustrated embodiments the maximum voltage will be only a small fraction of the normal rated voltage for composition resistances.

Although heat is the principal form of energy dissipated by a resistance, the power rating of composition resistances has been established in terms of an acceptable change in resistance rather than in terms of a temperature rise. This rating is usually for a change in resistance of 10% after 500 hours of a 1 /2 hour on, /2 hour olf, duty cycle at an ambient temperature of 40 C. Such resistances may be operated at full rated wattage only up to 40 C. ambient temperature. If the resistance is re quired to operate under higher surrounding temperature conditions, its power rating must be reduced. For example, at C. ambient temperature the power rating is out about in half. Higher quality resistances are rated at 70 C. ambient temperature and, of course, these resistances may be operated at full wattage up to 70 C. ambient temperature.

In the illustrated embodiment, a sensuously observable temperature, approximately 55 (3., is desired when a lamp burns out. Obviously, the ambient temperature for the heating element, which is dependent upon the heat dissipation of the lamp assembly, will be slightly higher, perhaps 57 C. Thus, if the energized heating element in these illustrated embodiments will dissipate of a watt, a standard grade (40 C. ambient temperature) composition resistance used as the heating element should be rated at approximately 1 watt. Either the bulk or film type composition resistances may be incorporated as the heating element in this invention.

It is understood that this invention is not to be limited to low impedance lamp assemblies of the type depicted in the drawings d discussed herein, but that this invention is adaptable to any plurality of low impedance elements in a series connection. Preferably it is adaptable to filamentary type low impedance elements having a relatively short life expectancy.

By this invention, a means has been provided for the safe positive identification of a burnt out incandescent lamp or any other low impedance element in a series connection. i' he disclosed Christmas tree lighting system application has numerous other practical advantages in that it may be manufactured without alteration of the present production equipment and it permits the simple and inexpensive conversion of existing consumer owned lighting systems.

It is understood that this invention is to be limited only by the scope of the claims appended hereto.

What I claim is:

1. An improved multiple element electrical system adapted for simultaneous energization by an electrical energy source comprising a plurality of low impedance filamentary lamp elements connected in series, each of said low impedance elements having a predetermined normal operation current requirement, the number of elements in said plurality being appropriate with respect to the output voltage of said electrical energy source to meet said normal operation current requirement; each of said low impedance filamentary elements having a visually perceptible luminosity during normal operation; a plurality of heat signaling means equal in number to the first said plurality, each of said heat signaling means having a respective heat dissipation surface area associated therewith, each of said heat signaling means connected in parallel with a difierent element in said plurality of low impedance elements, each of said heat signaling means having an impedance substantially greater than the total impedance of said series connected low impedance elements such that the remaining n-ondefective elements are maintained current conductive and below visually perceptible luminosity and are characterized by the absence of significant external thermal activity when the current path through at least one of said series connected elements is interrupted to render said element defective, each of said heat signaling means having a heat dissipation characteristic such that a temperature rise occurs on said surface area of the heat signaling means associated with a defective element, said temperature rise producing a touch perceptible temperature difference with respect to any of said remaining nondefective elements.

2. An improved multiple element electrical system adapted for simultaneous energization by an electrical energy source comprising a plurality of low impedance filamentary elements connected in series, each of said low impedance elements having a predetermined normal operation current requirement, the number of elements in said plurality being appropriate with respect to the output voltage of said electrical energy source to meet said normal operation current requirement; each of said low impedance filamentary elements having a visually perceptible luminosity during normal operation; a plurality of heat signaling means equal in number to the first said plurality, each of said heat signaling means having a respective heat dissipation surface area associated therewith, each of said heat signaling means connected in parallel a different element in said plurality of low impedance elements, each of said heat signaling means having an impedance substantially greater than the total impedance of said series connected low impedance elements such that the remaining nondefective elements are maintained current conductive and below visually perceptible luminosity and are characterized by the absence of significant external thermal activity when the current path through at least one of said series connected elements is interrupted to render said element defective, each of said heat signaling means having a heat dissipation characteristic such that a temperature rise occurs on said surface area of the heat signaling means associated with a defective element, said temperature rise producing a touch perceptible temperature difierence with respect to any of said remaining nondefective elements.

3. An improved multiple element electrical system adapted for simultaneous energization by an electrical energy source comprising a plurality of low impedance elements connected in series, each of said low impedance elements having a predetermined normal operation current requirement, the number of elements in said plurality being appropriate with respect to the output voltage of said electrical energy source to meet said normal operation current requirement; each of said low impedance elements having an operative energization state during which said normal operation current flows therethrough and an inoperative energization state during which a significant amount of current less than of said normal operation current flows therethrough, a plurality of heat signaling means equal in number to the first said plurality, each of said heat signaling means having a respective heat dissipation surface area associated therewith, each of said heat signaling means connected in parallel with a different element in said plurality of low impedance elements, each of said heat signaling means having an impedance substantially greater than the total impedance of said series connected low impedance elements such that the remaining nondefective elements are maintained in said inoperative energization state and are characterized by the absence of significant external thermal activity when the current path through at least one of said series connected elements is interrupted to render said element defective, each of said heat signaling means having a heat dissipation characteristic such that a temperature rise occurs on said surface area of the heat signaling means associated with a defective element, said temperature rise producing a touch perceptible temperature difference with respect to any of said remaining nondefective elements.

References Cited in the file of this patent UNITED STATES PATENTS 1,954,355 Handy Apr. 10, 1934 2,152,228 Waters Mar. 28, 1939 2,211,884 Davis Aug. 20, 19,40 

